Preheat the oven to 325°F. Coat a 9 x 13-inch baking dish with nonstick cooking spray. Set aside.
Place sweet potatoes in a heavy-bottomed pot and cover with salted water. Bring to a boil over high heat. Once water is boiling, reduce heat to medium-low, cover with lid, and simmer for 20 minutes, or until sweet potatoes are fork-tender. Drain water and allow sweet potatoes to become cool enough to handle. Remove and discard skins.
In a large mixing bowl, using an electric hand mixer, beat potatoes until smooth. Stir in butter, ground cinnamon, ground nutmeg, half and half, and milk. Mix until well combined and smooth.
Spread mashed sweet potatoes across a 9 x 13-inch baking dish and bake in the oven until thoroughly heated, approximately 20 minutes.
Top evenly with bacon pieces, return to oven and bake for an additional 5 minutes.